Can a Red filter make you miss infinity focus?

[retcheto]

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Is it possible for a red filter to make a lens miss sharpness at infinity?

 

That seems to be what I'm seeing with my 50mm Summicron and my 135mm f4 Tele-elmar. My 28mm f2.8 Elmarit doesn't seem to have any problem. Since it's ASPH I'm guessing it has better chromatic correction perhaps.

 

What I mean is I'm taking shots of mountains at a distance, normally both lenses are very sharp focused at infinity. An orange filter (B+W 040) doesn't seem to affect them, but either of the 090 or 091 light red or deep red from B+W result in a loss of sharpness, the 091 more so.

 

With the 135mm some of it may be from longer exposures needed to compensate for light loss which might give me some more vibrations, even though I have a good tripod. Sometimes it's windy though.

 

I doubt this is happening with the 50mm though since that focal length should be more forgiving for a little shake (?)

 

Could I be getting a focus shift from the red filters that makes the focused image miss the sensor perhaps at infinity perhaps? My 28/2.8 has no problem, even with the deep red

Edited February 10, 2018 by retcheto

[rpittal]

A "true" apochromatic lens focus the three main wavelengths at the "same" point. A less-corrected achromatic lens is more centered on mid wavelengths (yellowish). With a red filter, most of the light hitting the sensor is at an extreme wavelength that can have varying amounts of correction, depending on the lens design. A rangefinder is focusing on the "normal" wavelengths, so the red light may not be striking the sensor at the same point. Live view focusing thru the filter would not have this effect and would be in focus.

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[retcheto]

Yes I'm familiar with the focus shift issue when using the rangefinder, but that's not what I'm referring to.

 

What I'm seeing is those two lenses cannot focus at infinity with a red filter, and it seems to get worse with the deep red vs the light red. It's possible it's simply camera shake from the longer exposure needed. The image appears to be sharp in Liveview, at least as sharp as you can tell with the relatively low resolution of the back screen, but when viewed at 100% on a real monitor I can see a loss of sharpness that I don't see with lighter filters, which makes me wonder if the focal plane is being thrown 'behind' the sensor or something strange like that

[01af]

Is it possible for a red filter to make a lens miss sharpness at infinity?

Yes, it can. A red filter's effect is similar to an IR filter, just weaker. For IR, many lenses have an extra index that is different from the regular focus index. When shooting through a deep red filter, try setting the infinity symbol half-way between the regular and the IR index ... in other words, try setting the lens to a slightly shorter distance than infinity.

[John Black]

Or, if using the M-246, use the EVF save some headaches.  It's not a great EVF, but it's plenty good for focusing landscapes.  If I'm shooting filters on the M-246, it's an EVF all the way.  Too many missed shots otherwise.

[IkarusJohn]

He’s focussing using Liveview.

 

If the image you’re focusing on is tack sharp on the LCD or in the EVF magnified, but the image is less sharp, then I can think of only two issues - motion blur or softness at the aperture setting. Certainly, not an issue with the filter (assuming it’s a high quality filter).

 

Try stopping down to f/4 or smaller, use a tripod and fire the shutter using a cable release and self-timer and see if you can achieve a sharp image.

[retcheto]

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Yes thanks for the advice. That's pretty much what the issue was, probably a little motion due to the longer exposure time needed. I focused on better tripod technique and was able to make it work better

[LeicaR10]

Retcheto,  I think you will find the articles written at Pebble Place might be of use.  Try:  http://www.pebbleplace.com/geartalk/2016_03_14.html  and try:  http://www.pebbleplace.com/geartalk/2016_07_04.html  and try:  http://www.pebbleplace.com/geartalk/2016_06_29.html    r/ Mark

[pico]

Is it possible for a red filter to make a lens miss sharpness at infinity?

 

The rangefinder does not know, nor care what filter is over the lens.

Nor does EVF!

 

A deep red filter will shift focus. Does your lens have an IR marking?

That's a hint.

Edited February 21, 2018 by pico

[IkarusJohn]

The rangefinder does not know, nor care what filter is over the lens.

Nor does EVF!

 

A deep red filter will shift focus. Does your lens have an IR marking?

That's a hint.

I think he gets that, Pico. He’s focussing using live view, not the rangefinder. Edited February 21, 2018 by IkarusJohn

[retcheto]

Yes I was wondering whether focusing at infinity could be ruined with a filter, but the problem I had was camera shake